Low temperature reading 1998
#1
01-03-2019, 12:43 AM
Low temperature reading 1998
My 98 grand marquis coolant temp gauge only rises to the bottom hash of the operating tenperature range. It used to live in the direct middle of the operating range when warmed up until recently. Why does it appear that my marquis is running cold or just at the lowest temp within the operating range?
Heat blows hot. Thermostat was replaced because I assumed it was stuck open but nothing changed. I also noticed that the coolant overflow tank never really gets hot enough to pressurize. I can open the cap immediately after a long drive. I suspect the coolant system may not be holding pressure as the upper hose is warm but soft after a drive.
I have not noticed any coolant loss. No changes in how the car drives. No check engine light. Should I be concerned or is this something to look into?
Considering checking the coolant overflow pressure cap, and pressure testing the system. Could air in system cause this? Bad gauge and car temp is actually up to spec? Dont know where to start.
Appreciate all input.
Heat blows hot. Thermostat was replaced because I assumed it was stuck open but nothing changed. I also noticed that the coolant overflow tank never really gets hot enough to pressurize. I can open the cap immediately after a long drive. I suspect the coolant system may not be holding pressure as the upper hose is warm but soft after a drive.
I have not noticed any coolant loss. No changes in how the car drives. No check engine light. Should I be concerned or is this something to look into?
Considering checking the coolant overflow pressure cap, and pressure testing the system. Could air in system cause this? Bad gauge and car temp is actually up to spec? Dont know where to start.
Appreciate all input.
#2
01-03-2019, 11:24 AM
The Factory Shop Manual says that your '98 Marquis requires a 195 F Thermostat -- the emission controls are designed to work best at 195f, so.USE NO OTHER TEMPERATURES !!!
The Motorcraft (RT1234) Thermostat is the "replacement"" unit -- BUT -- it is NOT the same part as the original unit, which is NO LONGER AVAILABLE...
The original part was replaced by the Motorcraft #1234, which is a 190 F thermostat, and it runs 5 degrees colder than the original part.
The 5 degrees difference DOES make a difference -- in quicker warm-ups, faster emission controls response, improved fuel mileage, and less engine wear..
Your engine temp gauge is very sensitive, and a 5-degree difference is visible on the gauge needle..
Correct Thermostat = Part # Stant -13399 - 195 F -- The Stant Products are made in the USA for over 100 years, with a reputation for top quality and engineering.
Correct Thermostat Gasket = Part # Motorcraft RG 571
If the thermostat was changed with no difference in gauge reading, the problem is most likely a failed coolant tank pressure cap.
REPLACE the Coolant Tank Pressure Cap -- it's cheap insurance.
Part # = MOTORCRAFT RS527 - 16 psi..
I got the right parts from RockAuto.com .
I have installed and tested many types/temperatures of thermostats and gaskets in the 4.6-Liter engine -- chasing the optimum temperatures and operating conditions for the V-8 engine
that operates under severe desert conditions, using an ACTRON CP9145 OBD II Scanner/Code Reader, which allows engine temps and other factors to be checked WHILE DRIVING.
The Motorcraft (RT1234) Thermostat is the "replacement"" unit -- BUT -- it is NOT the same part as the original unit, which is NO LONGER AVAILABLE...
The original part was replaced by the Motorcraft #1234, which is a 190 F thermostat, and it runs 5 degrees colder than the original part.
The 5 degrees difference DOES make a difference -- in quicker warm-ups, faster emission controls response, improved fuel mileage, and less engine wear..
Your engine temp gauge is very sensitive, and a 5-degree difference is visible on the gauge needle..
Correct Thermostat = Part # Stant -13399 - 195 F -- The Stant Products are made in the USA for over 100 years, with a reputation for top quality and engineering.
Correct Thermostat Gasket = Part # Motorcraft RG 571
If the thermostat was changed with no difference in gauge reading, the problem is most likely a failed coolant tank pressure cap.
REPLACE the Coolant Tank Pressure Cap -- it's cheap insurance.
Part # = MOTORCRAFT RS527 - 16 psi..
I got the right parts from RockAuto.com .
I have installed and tested many types/temperatures of thermostats and gaskets in the 4.6-Liter engine -- chasing the optimum temperatures and operating conditions for the V-8 engine
that operates under severe desert conditions, using an ACTRON CP9145 OBD II Scanner/Code Reader, which allows engine temps and other factors to be checked WHILE DRIVING.
Last edited by 95 MERC; 01-25-2019 at 08:11 AM. Reason: add content
#3
01-09-2019, 04:07 AM
Go with an OEM (MOTORCRAFT) stat. Quality varies widely with the aftermarkets that I had issues with many and they don't seem to last long.. 190 or 195 is not going to change the temperature gauge at all or engine performance, so how could you go wrong with OEM? Order a Motorcraft from Rockauto if you cannot find one locally. I like to drill a small hole (1/16 inch) in the thermostat, if there isn't already one, to act as a vent to allow any trapped air to be easily belched out. It won't have any effect on temperature from my experience.Y ou could have air or a sending unit which is out of spec. As suggested, a code scanner can give you live data and give you the actual running temperature of your coolant to verify.
Last edited by raski; 01-09-2019 at 04:12 AM.
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